1. Field of the Invention
The present invention relates to an electroluminescence (EL) device which is activated by an alternating current (AC), and more particularly, to an easy to fabricate and highly luminous EL device having an electrode made of transparent conductive polymer and Indium-Tin-Oxide (ITO) powder.
2. Description of the Prior Art
Referring to FIG. 1, a cross-sectional view of a conventional AC EL device which is used, for example, to illuminate a passive LCD (Liquid Crystal Display) from the back is shown. The EL device shown in FIG. 1 comprises a plurality of layers including a substrate 11, a back electrode layer 10, a dielectric layer 4, a phosphor layer 6, a front electrode layer 12, and a polymer protection layer 5. Briefly describing the procedures for making the conventional EL device shown in FIG. 1, the back electrode layer 10 is first formed on top of the substrate 11. The back electrode layer 10 is made of highly reflective metal such as silver or aluminum so that the light incident to the back electrode layer 10 may be reflected therefrom. Then, the dielectric layer 4 is formed on the back electrode layer 10, wherein the dielectric layer 4 is made either of a mixture of dielectric powder and binder or of a flexible dielectric thin film. Subsequently, the phosphor layer 6, comprising a mixture of phosphor powder 7 and binder, is formed on the dielectric layer 4. Similar materials are used for the binder of the phosphor layer 6 and that of the dielectric layer 4. It should be noted that in the conventional EL device, the phosphor powder particles 7 are surrounded by the dielectric material and, therefore, the phosphor powder particles 7 do not directly contact the front electrode layer 12 as will be described below. Then, an ITO thin film, which is made of In.sub.2 O.sub.3 and SnO.sub.2, is laminated on the phosphor layer 6 by using vacuum evaporation, to thereby form the front electrode layer 12. It should also be noted that the vacuum evaporation process is more complicated and costly compared with processes using materials in a liquid state. Lastly, polymer is spread on the front electrode layer 12 to form the protection layer 5. One of the problems encountered with the conventional EL device is that it has relatively low luminance, thereby somewhat limiting its applicability. The luminance of a currently available EL device is about 70-80 Cd/m.sup.2. However, an LCD backlighting device generally requires luminance over 100-150 Cd/m.sup.2. Especially, to illuminate a STN (Super Twisted Nematic) type LCD, luminance should be at least 120 Cd/m.sup.2, considering the loss of light. Another problem with the conventional EL device is related to the cost for manufacturing which can also limit the applicability of the device.
Therefore, there has been a need in the art for more luminous EL devices which have improved applicability and can be simply fabricated at a minimum cost.